I use pro audio power amps in my home theater. They provide tons of power for little money. There is one major downside though. Most models feature noisy fans, and for a good reason – pro audio power amps are often run at their limits, and many manufacturers prefer to err on the side of caution. For home use though, you can usually get away with replacing the built-in fans with quieter ones as long as the amp isn’t housed inside closed spaces with poor or no ventilation.
I have done three power amp fan mods so far, and each one was different. Let’s start with the easiest one first:
The Behringer iNuke NU6000DSP, a class D amp with built-in DSP. It can do about 2 x 2,000W into 4 ohm short-term, an inexpensive amp well suited for subwoofer duty.
The NU6000DSP uses dual 80 mm 12V fans. For this one, I used USB powered 80 mm fans and mounted the fans from the outside. Internal mounting meant drilling holes in the case, which I preferred not to. The USB connector is plugged into the AVR, and the fans start spinning when the AVR is turned on.
Up next, the Behringer iNuke NU3000DSP, smaller brother of iNuke NU6000DSP, is again a class D amp with built-in DSP. It can do about 2 x 500W into 4 ohm. When bridged, it can produce as much as 2,000W short-term into 4 ohm.
The NU3000DSP looks exactly like the NU6000DSP, but is shorter in depth. It uses an 80 mm 12V fan covered by a black cardboard shroud, which is lightly glued to the fan. The shroud appears to be designed to concentrate air flow to four transistors with small yellow heat-sinks. Once the shroud is removed, replacing the existing fan with a quieter version is easy. The fan connector needs to be fixed in place with a dab of hot glue though.
Finally, the fan mod that required the most effort is a Behringer KM750, a traditional class AB amp. I use this amp for my center channel speaker. It can do about 2 x 180W RMS into 4 ohm.
The KM750 has a 90 mm 24V fan mounted on an internal heat sink. As the heat sink is wide enough, I decided to use a 120 mm fan, which can spin slower (and quieter), but still move quite a bit of air. So, how do you mount a 120 mm fan to a heat sink with holes drilled for a 90 mm fan?
I had four options:
Since most quiet fans are 12V, an inexpensive buck converter is necessary to lower the 24V provided by the amp to 12V or less. In the end, the 120 mm fan wasn’t quiet enough at 12V, so I lowered the voltage to less than 10V until the fan noise was acceptable. Even in cases when you don’t need a buck converter, they can come handy to lower fan noise to exactly the level you want.
In the picture above, the buck converter can be seen on the bottom-right corner mounted on a suitable spot. I didn’t feel like drilling holes in the bottom of the case. There was already a screw hole for one of the feet, so I used that screw and some hot glue which doubled as insulation to hold the buck converter in place. Yes, I know the proper way to mount a PCB is to use standoffs, but if the amp doesn’t move much and isn’t driven hard all the time, hot glue is probably OK.
…and that’s a wrap. Three different amps, three different ways to do fan mods. Hope you find this useful.
I have done three power amp fan mods so far, and each one was different. Let’s start with the easiest one first:
The Behringer iNuke NU6000DSP, a class D amp with built-in DSP. It can do about 2 x 2,000W into 4 ohm short-term, an inexpensive amp well suited for subwoofer duty.
The NU6000DSP uses dual 80 mm 12V fans. For this one, I used USB powered 80 mm fans and mounted the fans from the outside. Internal mounting meant drilling holes in the case, which I preferred not to. The USB connector is plugged into the AVR, and the fans start spinning when the AVR is turned on.
Up next, the Behringer iNuke NU3000DSP, smaller brother of iNuke NU6000DSP, is again a class D amp with built-in DSP. It can do about 2 x 500W into 4 ohm. When bridged, it can produce as much as 2,000W short-term into 4 ohm.
The NU3000DSP looks exactly like the NU6000DSP, but is shorter in depth. It uses an 80 mm 12V fan covered by a black cardboard shroud, which is lightly glued to the fan. The shroud appears to be designed to concentrate air flow to four transistors with small yellow heat-sinks. Once the shroud is removed, replacing the existing fan with a quieter version is easy. The fan connector needs to be fixed in place with a dab of hot glue though.
Finally, the fan mod that required the most effort is a Behringer KM750, a traditional class AB amp. I use this amp for my center channel speaker. It can do about 2 x 180W RMS into 4 ohm.
The KM750 has a 90 mm 24V fan mounted on an internal heat sink. As the heat sink is wide enough, I decided to use a 120 mm fan, which can spin slower (and quieter), but still move quite a bit of air. So, how do you mount a 120 mm fan to a heat sink with holes drilled for a 90 mm fan?
I had four options:
- Mount the fan by using just one hole and hope the fan wouldn’t move over time.
- Drill and tap new holes in the heat sink.
- Buy an adapter.
- 3D print an adapter.
Since most quiet fans are 12V, an inexpensive buck converter is necessary to lower the 24V provided by the amp to 12V or less. In the end, the 120 mm fan wasn’t quiet enough at 12V, so I lowered the voltage to less than 10V until the fan noise was acceptable. Even in cases when you don’t need a buck converter, they can come handy to lower fan noise to exactly the level you want.
In the picture above, the buck converter can be seen on the bottom-right corner mounted on a suitable spot. I didn’t feel like drilling holes in the bottom of the case. There was already a screw hole for one of the feet, so I used that screw and some hot glue which doubled as insulation to hold the buck converter in place. Yes, I know the proper way to mount a PCB is to use standoffs, but if the amp doesn’t move much and isn’t driven hard all the time, hot glue is probably OK.
…and that’s a wrap. Three different amps, three different ways to do fan mods. Hope you find this useful.
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